A person who speaks the truth, especially when the truth is contrary to conventional wisdom and goes against the norm. In the 14 century, a "soothsayer" was a person who spoke truth.
In the fable, "The Emperors New Clothes," the child who points out that the Emperor isn't wearing any clothes is a truthsayer.
Popularline from the TV show, "Drake & Josh", where Josh calls Drake a liar.
Josh: Drake, you made that whole story up!
Drake: No?
Josh: YOU, started that fight!
Drake: You callin' me a liar?!
Josh: I ain't calling you a truther!
1. An exaggeration so big that it creates a black hole no truth can enter
2. Bullshit
Apple salesman: The iPhone 7 has every feature anyone could possibly want!
Jason: Bullshit, what about the headphone jack?
Mike: Chill, he's just using a truthful hyperbole.
Jason: So, bullshit?
Bob: Sounds like bullshit to me.